Catoptric projection optical system

ABSTRACT

A catoptric projection optical system for projecting a pattern on an object surface onto an image surface includes plural mirrors, wherein a second mirror from the image surface through the optical path receives convergent pencil of rays, and has a paraxial magnification of −0.14 or smaller.

This is a divisional of prior application Ser. No. 10/783,788, filed onFeb. 20, 2004, now pending, which is hereby incorporated by reference.

This application claims a benefit of priority based on Japanese PatentApplication No. 2003-044891, filed on Feb. 21, 2003, which is herebyincorporated by reference herein in its entirety as if fully set forthherein.

BACKGROUND OF THE INVENTION

The present invention relates generally to an exposure apparatus, andmore particularly to a reflection type or catoptric projection opticalsystem, and an exposure apparatus using the same which use ultraviolet(“UV”) and extreme ultraviolet (“EUV”) light to expose an object, suchas a single crystal substrate for a semiconductor wafer, and a glassplate for a liquid crystal display (“LCD”).

Recent demands for smaller and lower profile electronic devices haveincreasingly demanded finer semiconductor devices to be mounted ontothese electronic devices. For example, the design rule for mask patternshas required that an image with a size of a line and space (“L & S”) ofless than 0.1 μm be extensively formed. It is expected to requirecircuit patterns of less than 80 nm in the near future. L & S denotes animage projected onto a wafer in exposure with equal line and spacewidths, and serves as an index of exposure resolution.

A projection exposure apparatus as a typical exposure apparatus forfabricating semiconductor devices includes a projection optical systemfor exposing a pattern on a mask or a reticle, onto a wafer. Thefollowing equation defines the resolution R of the projection exposureapparatus (i.e., a minimum size for a precise image transfer) where λ isa light-source wavelength and NA is a numerical aperture of theprojection optical system: $\begin{matrix}{R = {k_{1} \times \frac{\lambda}{NA}}} & (1)\end{matrix}$

As the shorter the wavelength becomes and the higher the NA increases,the higher or finer the resolution becomes. The recent trend hasrequired that the resolution be a smaller value; however it is difficultto meet this requirement using only the increased NA, and the improvedresolution expects use of a shortened wavelength. Exposure light sourceshave currently been in transition from KrF excimer laser (with awavelength of approximately 248 nm) and ArF excimer laser (with awavelength of approximately 193 nm) to F₂ excimer laser (with awavelength of approximately 157 nm). Practical use of the EUV light isbeing promoted as a light source.

As a shorter wavelength of light narrows usable glass materials fortransmitting the light, it is advantageous for the projection opticalsystem to use reflective elements, i.e., mirrors instead of refractiveelements, i.e., lenses. No applicable glass materials have been proposedfor the EUV light as exposure light, and a projection optical systemcannot include any lenses. It has thus been proposed to form a catoptricprojection optical system only with mirrors (e.g., multilayer mirrors).

A mirror in a catoptric reduction projection optical system forms amultilayer coating to enhance reflected light and increase reflectance.The multilayer mirror is characterized in that when it is optimized soas to provide high reflectance to light at a small incident angle, itcan provide high reflectance to high at a large incident angledistribution, whereas when it is optimized so as to provide highreflectance to light at a large incident angle, it cannot provide highreflectance to only light at a small incident angle distribution.

More specifically, a multilayer mirror including 40 layers of molybdenumand silicon at a uniform period has an incident-angle range forreflectance of 60% or greater of 0° to 13° when the multilayer mirror isoptimized to the incident angle of 0°, and 10° to 17° when themultilayer mirror is optimized to the incident angle of 15°. Amultilayer coating with a complex structured, such as a gradedmultilayer coating that modulates a period of the multilayer accordingto positions, needs for a large incident angle distribution.

The smaller number of mirrors is desirable to increase reflectance forthe entire optical system. In addition, the projection optical systempreferably uses the even number of mirrors to avoid mechanicalinterference between a mask and wafer by arranging them at oppositesides with respect to a pupil.

As the EUV exposure apparatus has requires a smaller critical dimensionor resolution than a conventional one, higher NA is necessary (e.g., upto 0.2 for a wavelength of 13.4 nm). Nevertheless, conventional three orfour mirrors have a difficulty in reducing wave front aberration.Accordingly, the increased number of mirrors, such as six, as well asuse of an aspheric mirror, is needed so as to increase the degree offreedom in correcting the wave front aberration. Hereinafter, such anoptical system is referred to as a six-mirror system in the instantapplication. The six-mirror system has been disclosed, for example, inU.S. Pat. No. 6,033,079, and International Publication No. WO02/056114A2.

U.S. Pat. No. 6,033,079 discloses two typical six-mirror catoptricprojection optical systems, which receive light from the object surface,form an intermediate image via first to fourth reflective surfaces, andre-form the intermediate image on an image surface via a convex fifthreflective surface and a concave sixth reflective surface. Such astructure contributes to high NA by enlarging and introducing light tosixth reflective surface and condensing the entire light on the imagesurface. Thus, the sixth reflective surface has a large effectivediameter. The intermediate image should be formed after the fourthreflective surface to introduce the light into the fifth reflectivesurface while preventing the sixth reflective surface from shielding thelight.

In this case, divergent light enters the fifth reflective surface,increasing the incident-angle distribution on the fifth reflectivesurface. The first embodiment discloses an optical system that has anarc-shaped image with a width of 1 mm and NA=0.25, and the maximumincident angle is 17.1° and the minimum incident angle is 0.4° on thefifth reflective surface. Therefore, the incident-angle distribution is16.7°.

As a consequence, a distribution between the maximum and minimumincident angles on the fifth reflective surface significantlydeteriorates the reflectance and lowers the throughput on the abovemultilayer coating.

On the other hand, International Publication No. WO 02/056114A2 alsodiscloses a six-mirror catoptric projection optical system. Differentfrom ones disclosed in U.S. Pat. No. 6,033,079, this catoptricprojection optical system forms an intermediate image after the secondreflective surface and introduces roughly collimated light into thefifth reflective surface. This catoptric projection optical systemsomewhat improves an incident angle by introducing collimated light intothe fifth reflective surface. For example, for an arc-shaped field withNA=0.25 and a width of 2 mm, the maximum incident angle is 17° and theminimum incident angle is 5.5° on the fifth reflective surface.Therefore, the incident-angle distribution is 11.4°.

Still, this incident-angle distribution is not sufficiently small, andthe deteriorated reflectance on the fifth reflective surface lowersthroughput. In addition, the first concave reflective surface increasesan angle between exit light from the first reflective surface and theoptical axis, causing the third and fourth reflective surfaces to haveextremely large effective diameters. In particular, an effectivediameter of the fourth reflective surface is assumed to be 650 mm whenNA is made 0.25, and thus is not viable due to the large size of theapparatus and difficult processing measurements.

In view of the current inefficient EUV light source, high throughputneeds an improvement of the deteriorated reflectance on the fifthreflective surface.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an exemplified object of the present invention toprovide a six-mirror catoptric projection optical system with a high NAand excellent imaging performance, and an exposure apparatus using thesame, which are applicable to the EUV lithography, and reduce a maximumeffective diameter and an overall length of the optical system.

A catoptric projection optical system of one aspect according to thepresent invention for projecting a pattern on an object surface onto animage surface includes plural mirrors, wherein a second mirror from theimage surface through the optical path receives convergent pencil ofrays, and has a paraxial magnification of −0.14 or smaller. A catoptricprojection optical system of another aspect according to the presentinvention for projecting a pattern on an object surface onto an imagesurface includes plural mirrors, wherein a second mirror from the imagesurface through the optical path receives convergent pencil of rays, andan angle between two marginal rays of the convergent pencil of raysplane is 3° or greater in meridional plane when the catoptric projectionoptical system has a numerical aperture of 0.25 or greater.

The catoptric projection optical system includes, for example, six ormore mirrors. A third mirror from the image surface through the opticalpath may have the largest effective diameter among the plural mirrors.All of the plural mirrors may be aspheric mirrors including a multilayercoating that reflect light having a wavelength of 20 nm or smaller. Thecatoptric projection optical system may project light from a reflectionmask that is arranged on the object surface. The catoptric projectionoptical system may be non-telecentric at a side of object surface.

A catoptric projection optical system of still another aspect accordingto the present invention for projecting a pattern on an object surfaceonto an image surface includes six mirrors that include, in order fromthe object surface to the image surface on an optical path, a firstmirror, a second mirror, a third mirror, a fourth mirror, a fifthmirror, and a sixth mirror to sequentially reflect light, wherein thefirst mirror has a convex or plane shape, and the fifth mirror receivesconvergent pencil of rays.

The fifth mirror preferably has a paraxial magnification of −0.14 orsmaller. An angle between two marginal rays of the convergent pencil ofrays received by M5 is 3° or greater in meridional plane when thecatoptric projection optical system has a numerical aperture of 0.25 orgreater.

The fifth mirror may have a paraxial magnification between −30 and −0.4.The catoptric projection optical system may include, in order of fromthe object surface to the image surface, the second mirror, the firstmirror, the fourth mirror, the sixth mirror, the third mirror and thefifth mirror, wherein an intermediate image may be formed between thefourth and third mirrors. The intermediate image may be formed betweenthe fourth and sixth mirrors or between the six and third mirrors.

The six mirrors may form an intermediate image. The intermediate imagemay not accord with a surface of one of the six mirrors. All of sixmirrors may be arranged between the object surface and the imagesurface. The second mirror from the image surface through the opticalpath may have a paraxial magnification between −30 and −0.4. An anglebetween two marginal rays of the convergent pencil of rays received bythe second mirror from the image surface is 9° or greater in meridionalplane, when the catoptric projection optical system has a numericalaperture of 0.25.

An exposure apparatus of another aspect according to the presentinvention includes the above catoptric projection optical system, and amask stage that supports a mask having the pattern, and positions thepattern on the mask onto the object surface, a wafer stage that supportsan object having a photosensitive layer, and positions thephotosensitive layer on the image surface, and a mechanism forsynchronously scanning the mask stage and the wafer stage while the maskis illuminated by light having a wavelength of 20 nm or smaller.

An exposure apparatus of still another aspect according to the presentinvention includes an illumination optical system for illuminating apattern with light from a light source, and the above catoptricprojection optical system. The catoptric projection optical system mayproject light reflected on the pattern, onto the image surface.

A device fabricating method includes the steps of exposing an objectusing the above exposure apparatus, and developing the exposed object.Claims for a device fabricating method for performing operations similarto that of the above exposure apparatus cover devices as intermediateand final products. Such devices include semiconductor chips like an LSIand VLSI, CCDs, LCDs, magnetic sensors, thin film magnetic heads, andthe like.

Other objects and further features of the present invention will becomereadily apparent from the following description of the preferredembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structure of a catoptric projection optical systemof one embodiment according to the present invention.

FIG. 2 is a schematic structure of a catoptric projection optical systemof another embodiment according to the present invention.

FIG. 3 is a schematic structure of an exposure apparatus that includesthe catoptric projection optical system shown in FIG. 1.

FIG. 4 is a flowchart for explaining a method for fabricating devices(semiconductor chips such as ICs, LSIs, and the like, LCDs, CCDs, etc.).

FIG. 5 is a detailed flowchart for Step 4 of wafer process shown in FIG.4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of catoptric projection optical systems100 and 100A and an exposure apparatus 200 as one aspect of the presentinvention with reference to the accompanying drawings. The samereference numeral in each figure denotes the same element, and adescription thereof will be omitted. Here, FIG. 1 is a schematicstructure of the catoptric projection optical system 100. FIG. 2 is aschematic structure of the catoptric projection optical system 100A.Unless otherwise specified, the catoptric projection optical system 100generalizes the catoptric reduction projection optical system 100A.

Referring to FIG. 1, the inventive catoptric projection optical system100 reduces and projects a pattern on an object surface (MS), such as amask surface, onto an image surface (W), such as a substrate surface andan object surface to be exposed. The catoptric projection optical system100 is an optical system particularly suitable for the EUV light (with awavelength between 10 nm and 15 nm, preferably between 13.4 nm and 13.5nm).

The inventive catoptric projection optical system 100 has six mirrorsincluding, in order of sequential reflections of light from an objectsurface MS, a first (convex or plane) mirror M1, a second (concave)mirror M2, a third (plane) mirror M3, a fourth (concave) mirror M4, afifth (convex) mirror M5, and a sixth (concave) mirror M6. The first andsecond mirrors M1 and M2 form an intermediate image IM, which is in turnre-imaged on an image surface W by the third to six mirrors M3 to M6.

Since the fifth mirror M5 usually has a large incident angle and a largeincident-angle distribution, deteriorated reflectance becomes a problemfor an applied multilayer coating. However, the inventive catoptricprojection optical system 100 maintains the reflectance by introducingconvergent pencil of rays into the fifth mirror M5.

The catoptric projection optical system 100 does not accord the mirrorposition with the intermediate image IM surface, reducing aberrationthat would otherwise occur due to the dust and energy concentrations.Since the catoptric projection optical system 100 arranges an aperturestop on the second mirror M2, and facilitates an arrangement of theaperture stop. In addition, the catoptric projection optical system 100arranges all the mirrors between the object surface MS and the imagesurface W, and facilitates arrangements of mask and wafer stages, etc.

The inventive catoptric projection optical system 100 also hasadvantages in that the fourth mirror M4 has a maximum but reducedeffective diameter among the six mirrors, and the overall length of theoptical system is short, as described later.

The catoptric projection optical system 100 is so non-telecentric tolight incident upon the first mirror M1 from the object surface MS, andtelecentric to the exit light at the image surface W side. For example,the object surface MS side needs a certain incident angle, in order toilluminate a mask arranged on the object surface MS through anillumination optical system, and to form an image on a wafer located atthe image surface W. On the other hand, the image surface W side ispreferably telecentric to reduce a change of magnification, for example,when the wafer located at the object surface MS moves in the opticalaxis direction.

The inventive projection optical system 100 is arranged substantially asa coaxial optical system that is axially symmetrical around one opticalaxis, has an advantage in that an arc-shape image field around theoptical axis can preferably correct aberration. However, the six mirrorsin the catoptric projection optical system 100 do not have to bearranged perfectly coaxial for aberrational corrections or adjustments.For example, they may slightly decenter for aberrational improvements orimprove the degree of freedom in arrangement.

The catoptric projection optical system is indispensable to the EUVoptical system, and required to reduce light shielding at the imagesurface W side as higher NA is demanded. In order to form a desiredoptical system with high NA and reduced light shielding, the instantembodiment forms the intermediate image IM between the second and thirdmirrors M2 and M3, and enhances powers of the fifth and sixth mirrors M5and M6. Preferably, the fifth and sixth mirrors M5 and M6 are convex andconcave mirrors, respectively, for imaging with high NA and maintainedback focus. Here, the “back focus” means an interval between the surfaceclosest to the image surface and the image surface (W).

In the catoptric projection optical system 100, the first mirror M1 ispreferably a convex or plane mirror to reduce an angle between the exitlight from the first mirror M1 and the optical axis. Where r1 to r6 areradii of curvature of the first to sixth mirrors M1 to M6, the sum ofPetzval terms should be zero or nearly zero as expressed by Equations 2and 3. While the fifth mirror M5 is a convex mirror, use of a convexmirror or a plane mirror for other mirrors would have an effect ofreducing the sum of Petzval terms, or easily flattening the imagesurface. $\begin{matrix}{{\frac{1}{r_{1}} - \frac{1}{r_{2}} + \frac{1}{r_{3}} - \frac{1}{r_{4}} + \frac{1}{r_{5}} - \frac{1}{r_{6}}} \approx 0} & (2) \\{{\frac{1}{r_{1}} - \frac{1}{r_{2}} + \frac{1}{r_{3}} - \frac{1}{r_{4}} + \frac{1}{r_{5}} - \frac{1}{r_{6}}} = 0} & (3)\end{matrix}$

Although the inventive catoptric projection optical system 100 includessix mirrors, at least one or more mirrors may have an aspheric surface.Equation 4 defines a general aspheric shape. As a mirror having anaspheric surface advantageously facilitates a correction of aberration,the aspheric surface is preferably applied to many possible (desirably,six) mirrors. $\begin{matrix}{Z = {\frac{{ch}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}h^{2}}}} + {A\quad h^{4}} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Fh}^{14} + {Gh}^{16} + {Hh}^{18} + {Jh}^{20} + \ldots}} & (4)\end{matrix}$where “Z” is a coordinate in an optical-axis direction, “c” is acurvature (i.e., a reciprocal number of the radius r of curvature), “h”is a height from the optical axis, “k” a conic constant, “A” to “J” areaspheric coefficients of 4^(th) order, 6^(th) order, 8^(th) order,10^(th) order, 12^(th) order, 14^(th) order, 16^(th) order, 18^(th)order, 20^(th) order, respectively.

A multilayer coating for reflecting the EUV light is applied onto asurface of each of the first to sixth mirrors M1 to M6, and serves toenhance the light. A multilayer coating that can reflect the EUV lighthaving a wavelength of 20 nm or smaller can include, for example, aMo/Si multilayer coating including alternately laminated molybdenum (Mo)and silicon (Si) layers or a Mo/Be multilayer coating includingalternately laminating molybdenum (Mo) and beryllium (Be) layers. Anoptimal material is selected according to wavelengths to be used. Ofcourse, the present invention does not limit the multilayer coating tothe above materials, and may use any multilayer coating that has anoperation or effect similar to that of the above.

A description will now be given of illumination experiment results usingthe inventive catoptric projection optical systems 100 and 100A. InFIGS. 1 and 2, MS is a reflection mask located at the object surface,and W is a wafer located at the image surface.

The catoptric projection optical systems 100 and 100A illuminate themask MS using an illumination system (not shown) for emitting the EUVlight with a wavelength of about 13.4 nm, and reflects the reflected EUVlight from the mask MS via the first (convex or plane) mirror M1, thesecond (concave) mirror M2, the third (plane) mirror M3, the fourth(concave) mirror M4, the fifth (convex) mirror M5, and the sixth(concave) mirror M6 in this order. Then, a reduced image of the maskpattern is formed on the wafer W located at the image surface.

The catoptric projection optical systems 100 and 100A form theintermediate image IM between the second and third mirrors M2 and M3,and re-form the intermediate image IM on the wafer W via the third tosix mirrors M3 to M6.

However, the first mirror M1 has various possible shapes, and the firstmirror has a convex mirror in the catoptric projection optical system100 shown in FIG. 1 and a plane mirror in the catoptric projectionoptical system 100A shown in FIG. 2.

The catoptric projection optical system 100 shown in FIG. 1 has anumerical aperture at the image side NA=0.24, a reduction=1/4, an objectpoint of 128 to 136 mm, and an arc-shaped image field with a width of 2mm. Table 1 indicates the numerical values (such as radius of curvature,surface intervals, and coefficients of aspheric surfaces) of thecatoptric projection optical system 100 shown in FIG. 1. TABLE 1 MIRRORRADII OF CURVATURE SURFACE INTERVALS NUMBERS (mm) (mm) MS(MASK) ∞491.89136 M1 3842.26663 −391.89136 M2 632.52970 782.33141 M3 ∞−340.56806 M4 587.99023 347.08332 M5 179.04357 −296.95531 M6 384.58260340.95531 W(WAFRR) ∞ ASPHERIC COEFFICIENTS K A B M1 −267.466169 −0.780043944E−8   0.413260127E−12 M2 −2.62843602  0.1771126504E−8  −0.104963421E−13 M3 0 −0.181104227812E−8   0.35455238427E−13 M4−0.501489651051 −0.499638591354E−10  0.551481326761E−15 M50.652185965963 0.128818331391E−7 −0.122530514853E−11 M6 0.0422385684211 0.631614287722E−10  0.118302622927E−14 C D E M1    0.821038E−16   −0.2002547E−19   0.340695911E−23 M2 0.216367766343E−18−0.705067342902E−21  0.45932705835E−24 M3 −0.65672698442E−180.2525006259565E−22 −0.293865288006E−27 M4 0.621448231393E−19−0.685646752963E−24  −0.54845472391E−29 M5  0.12745886225E−15 0.157924483326E−18 −0.265980125498E−21 M6  0.26360018168E−19−0.553148373653E−23  0.953035608666E−27

Aberrations that do not include manufacture errors in the catoptricprojection optical system 100 shown in FIG. 1 are wave front aberrationof 55 λrms, and static distortion of 0.93 nmPV.

The catoptric projection optical system 100 uses the first convex mirrorM1, thus reduces an angle between the exit light from the first mirrorM1 and the optical axis, and reflects the light near the optical axis.In addition, an intersection between the light from the second mirror M2to the third mirror M3 and the light from the fourth mirror M4 to thefifth mirror M5 maintains the light close to the optical axis. As aresult the maximum effective diameter is about 430 mm, which isextremely small and advantageous to the processing measurements. Thecatoptric projection optical system 100 prevents a problem of lightshielding on the sixth mirror M6 that has a large effective diameter,which would occur when the light is reflected around the optical axis,by forming the intermediate image IM between the second mirror M2 andthe third mirror M3.

The catoptric projection optical system 100 has an overall length of 933mm and a small mirror's effective diameter. Therefore, the mirror barrelfor the catoptric projection optical system 100 becomes small. It isnecessary to maintain the inside of the mirror barrel vacuum, since theair absorbs the EUV light. The small capacity of the mirror barrelfacilitates maintenance of high vacuum, and reduces a loss of the EUVlight due to absorptions by gas.

Table 2 shows characteristics of light's incident angles to respectivemirrors when NA is 0.25: TABLE 2 MIRROR MINIMUM NUMBERS MAXIMUM VALUESVALUES DISTRIBUTIONS M1 12.06° 4.26° 8.34° M2 9.15° 6.22° 2.93° M314.07° 0.58° 13.49° M4 7.68° 6.64° 1.03 M5 17.95° 13.08° 4.88° M6 6.42°3.03° 3.39°

Referring to Table 2, the fifth mirror M5 can maintain small the maximumvalue of the incident angle, and very small distribution of the incidentangle by receiving the convergent pencil of rays. This configurationprevents a deterioration of reflective performance of the fifth mirrorM5 when a multilayer coating is applied onto the fifth mirror M5. Thefifth mirror M5 in the instant embodiment has a paraxial magnificationof −0.61, and an angle of the marginal ray of 14° when converted into NAof 0.25. Thus, the catoptric projection optical system 100 prevents adeterioration of reflective performance for an application of amultilayer coating, by reducing an incident-angle distribution for amirror that has a large incident angle, and by reducing a maximum valueof the incident angle for a mirror that has a large incident-angledistribution.

On the other hand, the catoptric projection optical system 100A shown inFIG. 2 has a numerical aperture at the image side NA=0.25, areduction=1/4, an object point of 126 to 130 mm, and an arc-shaped imagesurface with a width of 1 mm. Table 3 indicates the numerical values(such as radius of curvature, surface intervals, and coefficients ofaspheric surfaces) of the catoptric projection optical system 100A shownin FIG. 2. TABLE 3 MIRROR RADII OF CURVATURE SURFACE INTERVALS NUMBERS(mm) (mm) MS(MASK) ∞ 630.39040422 M1 ∞ −414.889111869 M2 986.307001145.14669637 M3 ∞ −455.621212317 M4 919.99906 575.973223593 M5241.54161 −385.799698492 M6 472.69959 429.799698492 W (WAFER) ∞ 0ASPHERIC COEFFICIENTS K A B M1 0.0 0.392913766692E−8 −0.482700852306E−13 M2 5.71467204258 −0.74423961703E−9 −0.218940230513E−14 M3 0.0 0.117641302987E−9    0.437846210229E−13 M40.262054559486 0.102681269079E−9    0.402913796893E−15 M5−0.1333996647252 0.114059493627E−8    0.570575209799E−12 M60.029253097984 0.419098009587E−10   0.284038877645E−15 C D E M1   0.85841732904E−18 −0.573601920195E−22   −0.302379564719E−26 M2−0.164265249949E−17 0.123119917367E−20 −0.563252413767E−24 M3−0.209910470364E−17 0.274183093663E−22   0.515594464729E−27 M4−0.117081986791E−19 0.324154600714E−24 −0.374245169062E−29 M5−0.859772349117E−16 0.160541027121E−18 −0.162675556918E−21 M6−0.927844388002E−22 0.334753349725E−24  −0.39683041798E−28

Aberrations that do not include manufacture errors in the catoptricprojection optical system 100 a shown in FIG. 1 are wave frontaberration of 21 λrms, and static distortion of 2 nmPV.

The catoptric projection optical system 100A uses the first plane mirrorM1, thus reduces an angle between the exit light from the first mirrorM1 and the optical axis, and reflects the light near the optical axis.In addition, an intersection between the light from the second mirror M2to the third mirror M3 and the light from the fourth mirror M4 to thefifth mirror M5 maintains the light close to the optical axis. As aresult the maximum effective diameter is about 464 mm, which isextremely small and advantageous to the processing measurements. Thecatoptric projection optical system 100A prevents a problem of lightshielding on the sixth mirror M6 that has a large effective diameter,which would occur when the light is reflected around the optical axis,by forming the intermediate image IM between the second mirror M2 andthe third mirror M3.

Table 4 shows characteristics of light's incident angles to respectivemirrors when NA is 0.25: TABLE 4 MIRROR MINIMUM NUMBERS MAXIMUM VALUESVALUES DISTRIBUTIONS M1 10.97° 2.93° 8.04° M2 6.96° 6.49° 0.47° M311.24° 2.74° 8.50° M4 6.29° 3.61° 2.68¹¹ M5 18.10° 7.13° 11.0° M6 5.05°2.31° 2.74°

Referring to Table 4, the fifth mirror M5 receives convergent pencil ofrays, and has a small incident-angle distribution. In addition, thethird mirror M3 has a small incident-angle distribution. The fifthmirror M5 in the instant embodiment has a paraxial magnification of−0.15, and an angle of the marginal ray of 3.3° when converted into NAof 0.25.

Thus, the catoptric projection optical systems 100 and 100A introducesconvergent pencil of rays into the fifth mirror M5, and reduces anincident-angle distribution on the fifth mirror M5. Thereby, amultilayer coating of a simple structure can provide high reflectance,and prevents lowered throughput due to the deteriorated reflectance ofthe fifth reflective surface. In addition, the catoptric projectionoptical systems 100 and 100A use the first convex or plane mirror, andform the intermediate image IM by the first and second mirrors M1 andM2, thereby realizing a small effective diameter, a reduced size of anapparatus, and easy processing measurements.

From the above numerical examples of the catoptric projection opticalsystems 100 and 100A, the instant inventors have deduced as follows:

Since the fifth mirror M5 as a second mirror from the wafer (or imagesurface) has a paraxial magnification of −0.61 in the catoptricprojection optical system 100 and −0.15 in the catoptric projectionoptical system 100A, the instant embodiment preferably maintains aparaxial magnification of a second mirror from the wafer (or imagesurface) in the catoptric projection optical system to be −0.14 orsmaller, preferably, −0.4 or smaller. The lower limit is preferably −30or greater.

When the catoptric projection optical systems 100 and 100A have anumerical aperture of 0.25 or greater, the convergent pencil of raysincident upon the fifth mirror M5 and an angle between two marginal raysof the pencil of rays is 14° and 3.3°, respectively. Therefore, when thecatoptric projection optical system has a numerical aperture of 0.25 orgreater, the convergent pencil of rays incident upon the second mirrorfrom the wafer on the optical path has an angle of the marginal ray ofpreferably 3° or greater, more preferably 9° or greater.

Referring now to FIG. 3, a description will now be given of the exposureapparatus 200. FIG. 3 is a schematic structure of the exposure apparatus200. The exposure apparatus 200 is a projection exposure apparatus thatuses the EUV light (with a wavelength of, e.g., 13.4 nm) as illuminationlight for exposure, and provides a step-and-scan exposure.

The exposure apparatus 200 includes, as shown in FIG. 3, an illuminationapparatus 210, a mask MS, a mask stage 220 mounted with the mask MS, acatoptric projection optical system 100, an object W, a wafer stage 230mounted with the object W, and a controller 240. The controller 240 isconnected controllably to the illumination apparatus 210, the mask stage220 and the wafer stage 230.

At least the optical path through which the EUV light travels shouldpreferably be maintained in a vacuum atmosphere, although not shown inFIG. 3, since the EUV light has low transmittance for air. In FIG. 3,XYZ defines a three-dimensional space, and the direction Z is a normaldirection to the XY plane.

The illumination apparatus 210 uses arc-shaped EUV light (with awavelength of, for example, 13.4 nm) corresponding to an arc-shapedfield of the reflection type projection optical system, to illuminatethe mask MS, and includes a light source and illumination optical system(not shown). The illumination apparatus 210 may use any technology knownin the art for the light source and illumination optical system, and adetailed description thereof will be omitted. For example, theillumination optical system may include a condenser optical system, anoptical integrator, an aperture stop, a blade, etc., and use anytechnique conceivable to those skilled in the art.

The mask MS is a reflection or transmission mask, and forms a circuitpattern (or image) to be transferred. It is supported and driven by amask stage 220. The diffracted light emitted from the mask MS isprojected onto the object W after reflected by the projection opticalsystem 100. The mask MS and object W are arranged optically conjugatewith each other. Since the exposure apparatus 200 is a step-and-scanexposure apparatus, the mask MS and object W are scanned to transfer thepattern on the mask MS, onto the object W.

The mask stage 220 supports the mask MS and is connected to a mobilemechanism (not shown). The mask stage 220 may use any structure known inthe art. The mobile mechanism (not show) may use a linear motor, etc.,and drives the mask stage 220 in the direction Y so as to move the maskMS under control by the controller 240. The exposure apparatus 200 scanswhile synchronizes the mask MS and object W through the controller 240.

The catoptric projection optical system 100 is an optical system thatreduces and projects a pattern on the mask MS onto the image surface.The reflection type projection optical system 100 may use any of theabove embodiments, and a detailed description thereof will be omitted.Although FIG. 3 uses the reflection type optical system 100 shown inFIG. 1, the present invention is not limited to this illustrativeembodiment.

The object W is a wafer in this embodiment, but may be a LCD and anotherobject to be exposed. Photoresist is applied to the object W.

The object W is supported by the wafer stage 230. For example, the waferstage 230 uses a linear motor to move the object W in XYZ directions.The mask MS and object W are, for example, scanned synchronously undercontrol by the controller 240, and the positions of the mask stage 220and wafer stage 230 are monitored, for example, by a laserinterferometer and the like, so that both are driven at a constant speedratio.

The controller 240 includes a CPU and memory (not shown) and controlsoperations of the exposure apparatus 200. The controller 240 iselectrically connected to (a mobile mechanism (not shown) for) the maskstage 220, and (a mobile mechanism (not shown) for) the wafer stage 230.The CPU includes a processor regardless of its name, such as an MPU, andcontrols each module. The memory includes a ROM and RAM, and stores afirmware for controlling the operations of the exposure apparatus 200.

In exposure, the EUV light emitted from the illumination apparatus 210illuminates the mask MS, and the pattern on the mask MS onto the objectW. The instant embodiment provides a circular or arc-shaped image field,and scans the entire surface on the mask MS by scanning the mask MS andobject W with a speed ratio corresponding to the reduction ratio.

Referring to FIGS. 4 and 5, a description will now be given of anembodiment of a device fabricating method using the above mentionedexposure apparatus 200. FIG. 4 is a flowchart for explaining afabrication of devices (i.e., semiconductor chips such as IC and LSI,LCDs, CCDs, etc.). Here, a description will be given of a fabrication ofa semiconductor chip as an example. Step 1 (circuit design) designs asemiconductor device circuit. Step 2 (mask fabrication) forms a maskhaving a designed circuit pattern. Step 3 (wafer making) manufactures awafer using materials such as silicon. Step 4 (wafer process), which isreferred to as a pretreatment, forms actual circuitry on the waferthrough photolithography using the mask and wafer. Step 5 (assembly),which is also referred to as a post-treatment, forms into asemiconductor chip the wafer formed in Step 4 and includes an assemblystep (e.g., dicing, bonding), a packaging step (chip sealing), and thelike. Step 6 (inspection) performs various tests for the semiconductordevice made in Step 5, such as a validity test and a durability test.Through these steps, a semiconductor device is finished and shipped(Step 7).

FIG. 5 is a detailed flowchart of the wafer process in Step 4. Step 11(oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ion into the wafer. Step 15 (resist process)applies a photosensitive material onto the wafer. Step 16 (exposure)uses the exposure apparatus 200 to expose a circuit pattern on the maskonto the wafer. Step 17 (development) develops the exposed wafer. Step18 (etching) etches parts other than a developed resist image. Step 19(resist stripping) removes disused resist after etching. These steps arerepeated, and multilayer circuit patterns are formed on the wafer. Thedevice fabrication method of this embodiment may manufacture higherquality devices than the conventional one. Thus, the device fabricationmethod using the exposure apparatus 200, and the devices as finishedgoods also constitute one aspect of the present invention.

Further, the present invention is not limited to these preferredembodiments, and various variations and modifications may be madewithout departing from the scope of the present invention. For example,the reflection type projection optical system of this embodiment has acoaxial system having a rotationally symmetrical aspheric surface, butit may have a rotationally asymmetrical aspheric surface. The presentinvention is applicable a reflection type projection optical system fornon-EUV ultraviolet light with a wavelength of 200 nm or less, such asArF excimer laser and F₂ excimer laser, as well as to an exposureapparatus that scans and exposes a large screen, or that exposes withoutscanning.

Thus, the present invention can provide a six-mirror catoptricprojection optical system with a high NA and excellent imagingperformance, and an exposure apparatus using the same, which areapplicable to the EUV lithography, and reduce a maximum effectivediameter and an overall length of the optical system.

1. A catoptric projection optical system for projecting a pattern lightfrom a pattern on an object surface onto an image surface, saidcatoptric projection optical system comprising plural mirrors, wherein asecond mirror from the image surface along an optical path of thepattern light receives convergent pencil of rays, and has a paraxialmagnification of −0.14 or smaller.
 2. A catoptric projection opticalsystem according to claim 1, wherein said catoptric projection opticalsystem includes six or more mirrors.
 3. A catoptric projection opticalsystem according to claim 1, wherein a third mirror from the imagesurface through the optical path has the largest effective diameteramong the plural mirrors.
 4. A catoptric projection optical systemaccording to claim 1, wherein all of the plural mirrors are asphericmirrors including a multilayer coating that reflect light having awavelength of 20 nm or smaller.
 5. A catoptric projection optical systemaccording to claim 1, wherein said catoptric projection optical systemprojects light from a reflection mask that is arranged on the objectsurface.
 6. A catoptric projection optical system according to claim 1,wherein said catoptric projection optical system is non-telecentric at aside of object surface.
 7. A catoptric projection optical systemaccording to claim 1, wherein said plural mirrors form an intermediateimage.
 8. A catoptric projection optical system according to claim 7,wherein the intermediate image does not accord with a surface of one ofthe plural mirrors.
 9. A catoptric projection optical system accordingto claim 1, wherein all of said plural mirrors are arranged between theobject surface and the image surface.
 10. A catoptric projection opticalsystem according to claim 1, wherein the second mirror from the imagesurface through the optical path has a paraxial magnification between−30 and −0.4.
 11. A catoptric projection optical system according toclaim 1, wherein an angle between two marginal rays of said convergentpencil of rays is 9° or greater in meridional plane, when said catoptricprojection optical system has a numerical aperture of 0.25.
 12. Acatoptric projection optical system for projecting a pattern of lightfrom a pattern on an object surface onto an image surface, saidcatoptric projection optical system comprising plural mirrors, wherein asecond mirror from the image surface along an optical path of thepattern light receives convergent pencil of rays, and an angle betweentwo marginal rays of said convergent pencil of rays is 3° or greaterwhen said catoptric projection optical system has a numerical apertureof 0.25 or greater.
 13. A catoptric projection optical system accordingto claim 12, wherein said catoptric projection optical system includessix or more mirrors.
 14. A catoptric projection optical system accordingto claim 12, wherein a third mirror from the image surface through theoptical path has the largest effective diameter among the pluralmirrors.
 15. A catoptric projection optical system according to claim12, wherein all of the plural mirrors are aspheric mirrors including amultilayer coating that reflect light having a wavelength of 20 nm orsmaller.
 16. A catoptric projection optical system according to claim12, wherein said catoptric projection optical system projects light froma reflection mask that is arranged on the object surface.
 17. Acatoptric projection optical system according to claim 12, wherein saidcatoptric projection optical system is non-telecentric at a side ofobject surface.
 18. A catoptric projection optical system according toclaim 12, wherein said plural mirrors form an intermediate image.
 19. Acatoptric projection optical system according to claim 18, wherein theintermediate image does not accord with a surface of one of the pluralmirrors.
 20. A catoptric projection optical system according to claim12, wherein all of said plural mirrors are arranged between the objectsurface and the image surface.
 21. A catoptric projection optical systemaccording to claim 12, wherein the second mirror from the image surfacethrough the optical path has a paraxial magnification between −30 and−0.14.
 22. A catoptric projection optical system according to claim 12,wherein the angle between two marginal rays of said convergent pencil ofrays is 9° or greater, when said catoptric projection optical system hasa numerical aperture of 0.25. 23-31. (canceled)
 32. An exposureapparatus comprising: a catoptric projection optical system forprojecting a pattern light from a pattern on an object surface onto animage surface, said catoptric projection optical system comprisingplural mirrors, wherein a second mirror from the image surface alone anoptical path of the pattern light receives convergent pencil of rays,and has a paraxial magnification of −0.14 or smaller; a mask stage thatsupports a mask having the pattern, and positions the pattern on themask onto the object surface; a wafer stage that supports an objecthaving a photosensitive layer, and positions the photosensitive layer onthe image surface; and a mechanism for synchronously scanning said maskstage and said wafer stage while the mask is illuminated by light havinga wavelength of 20 nm or smaller.
 33. An exposure apparatus comprising:a catoptric projection optical system for projecting a pattern lightfrom a pattern on an object surface onto an image surface, saidcatoptric projection optical system comprising plural mirrors, wherein asecond mirror from the image surface along an optical path of thepattern light receives convergent pencil of rays, and an angle betweentwo marginal rays of said convergent pencil of rays is 3° or greaterwhen said catoptric projection optical system has a numerical apertureof 0.25 or greater; a mask stage that supports a mask having thepattern, and positions the pattern on the mask onto the object surface;a wafer stage that supports an object having a photosensitive layer, andpositions the photosensitive layer on the image surface; and a mechanismfor synchronously scanning said mask stage and said wafer stage whilethe mask is illuminated by light having a wavelength of 20 nm orsmaller.
 34. (canceled)
 35. An exposure apparatus comprising: anillumination optical system for illuminating a pattern with light from alight source; and a catoptric projection optical system for projecting apattern light from a pattern on an object surface onto an image surface,said catoptric projection optical system comprising plural mirrors,wherein a second mirror from the image surface along an optical path ofthe pattern light receives convergent pencil of rays, and has a paraxialmagnification of −0.14 or smaller.
 36. An exposure apparatus accordingto claim 35, wherein said projection optical system projects lightreflected on the pattern, onto the image surface.
 37. An exposureapparatus comprising: an illumination optical system for illuminating apattern with light from a light source; and a catoptric projectionoptical system for projecting a pattern light from a pattern on anobject surface onto an image surface, said catoptric projection opticalsystem comprising plural mirrors, wherein a second mirror from the imagesurface along an optical path of the pattern light receives convergentpencil of rays, and an angle between two marginal rays of saidconvergent pencil of rays is 3° or greater in meridional plane when saidcatoptric projection optical system has a numerical aperture of 0.25 orgreater.
 38. An exposure apparatus according to claim 37, wherein saidprojection optical system projects light reflected on the pattern, ontothe image surface. 39-40. (canceled)
 41. A device fabricating methodcomprising the steps of: exposing an object using an exposure apparatus;and developing the object that has been exposed, wherein said exposureapparatus includes: an illumination optical system for illuminating apattern with light from a light source; and a catoptric projectionoptical system for projecting a pattern light from then a pattern on anobject surface onto an image surface, said catoptric projection opticalsystem comprising plural mirrors, wherein a second mirror from the imagesurface along an optical path of the pattern light receives convergentpencil of rays, and has a paraxial magnification of −0.14 or smaller.42. A device fabricating method comprising the steps of: exposing anobject using an exposure apparatus; and developing the object that hasbeen exposed, wherein said exposure apparatus includes: an illuminationoptical system for illuminating a pattern with light from a lightsource; and a catoptric projection optical system for projecting apattern light from the pattern on an object surface onto an imagesurface, said catoptric projection optical system comprising pluralmirrors, wherein a second mirror from the image surface along an opticalpath of the pattern light receives convergent pencil of rays, and anangle between two marginal rays of said convergent pencil of rays is 3°or greater when said catoptric projection system has a numericalaperture of 0.25 or greater.